The present invention relates to an optical cable TV system.
Various cable TV systems, often called CATV, have been used for delivery of video signals to customers. Such cable TV systems have generally used coax cable to carry the video signals. Generally, such cables are limited to carrying 100 or fewer channels or video signals.
In an effort to increase the channel capacity of cable TV systems, various proposals have been made to send the video signals along optical fiber cables. Although such designs provide increased channel capacity beyond that of coax cable, channel capacity is still more limited than is desirable.
Apart from limitations on the channel capacity of cable TV systems, various other problems and constraints are generally present in cable TV systems.
Cable TV systems often use a relatively large number of amplifiers which are staggered along a trunk line in order to provide cable TV service. For example, there may be as many as seven amplifiers along a trunk line. Since each amplifier introduces at least some distortion, the quality of the video signal for those customers at the output of the seventh amplifier is much lower than the quality of the video signal for those customers closer to the beginning of the chain of amplifiers. Additionally, the failure of one of the amplifiers near the beginning of the chain will cause a loss of service for all customers further down the chain. If the first or second amplifier in the trunk line goes out of service, a very large number of customers will lose their cable TV service until repairs can be made.
Various designs have been used to provide on demand video services, often called pay per view. Although such services have been useful in allowing customers to customize the shows which they want to watch, present on demand features have certain disadvantages. Generally, such on demand or pay per view features provide the customer with a scrambled signal and the customer can watch the on demand or pay per view signal only if the customer signals the cable system that he or she wishes to watch the on demand signal. The cable TV system then usually sends data to the cable TV box at the viewer's house such that the cable TV box now unscrambles the signal. Since the signal is generally sent to the viewer's house whether the viewer has paid for it or not, there is a significant number of viewers who will buy descramblers or otherwise make efforts to view the program without paying for it. Such viewing of pirated pay per view or on demand video signals is a serious problem in the cable TV industry. Further, such an arrangement requires a descrambler, controllable by the cable TV company, within the cable TV box of all viewers. This increases the cost of equipment for the cable TV company, especially considering that a relatively sophisticated descrambler is needed at the customer's cable TV box to try to minimize the risk that the customer will buy or build their own descrambler in order to pirate the pay per view signals.
Generally, the need for various components, such as descramblers, associated with each cable TV box at the customer's home, increases the cost of hardware which must be provided by the cable TV company. On the other hand, it has not been practical generally to move some of the more sophisticated switching or descrambling components out of the customer's cable TV box since moving those components to a more central location would usually interfere with the ability of the customer to custom select features which he or she wishes to view.
Although various systems have been developed on cable TV to provide movies in response to customer's selections, such on demand or pay per view programming has been quite limited in flexibility. For example, if the viewer wishes to watch a pay per view movie when sitting down for television at 8:40 at night, the viewer may be discouraged to learn that the pay per view movie which he or she was interested in started at 8:30. The customer then must start the movie 10 minutes late, wait until the next showing at 10:30, or simply forget about watching the pay per view movie that night. Since such movies or other pay per view video signals are shown only at a relatively limited number of times, the viewer must accommodate the cable TV system instead of the other way around.
A problem with various optical cable TV systems is a difficulty in providing adequate filtering which will filter out undesired optical signals with a high degree of rejection, while passing a desired optical signal. If one is to use an optical fiber for carrying video signals on different wavelengths of laser light, one must have a tuneable optical filter (difficult to achieve satisfactorily) in order to select the wavelength of laser light corresponding to the desired signal or one must have a plurality of dedicated optical filters (each optical filter dedicated to a single wavelength) and an arrangement for selecting from the outputs of the different dedicated optical filters. In either case, complexity, high cost, and other difficulties have generally been encountered.
Cable TV systems often provide arrangements whereby one can block transmission of a signal such that a local signal can be inserted. For example, if a nationwide cable channel is provided to various local cable TV systems, such local cable TV systems want to be able to insert local commercials. At designated times in the feed from the nationwide cable channel, blocks of time will be provided for the local cable TV company to insert a local commercial. Arrangements for removal and insertion of signals upon a channel are often quite complex and expensive. Further, such local insertions often must be made at several locations in order to cover a metropolitan area. This increases the hardware requirements for making such insertions and renders the process more complex.